exprt::with_source_location: conditionally copy source location

This helper will copy the source location from another expression, if it
has any. Implemented as a fluent interface, with a first specialisation
for array_exprt. Other expression types an use
with_source_location<X_exprt> or add specialisations.

Author: tautschnig

src/util/expr.h

@@ -98,6 +98,30 @@ class exprt:public irept
   const operandst &operands() const
   { return (const operandst &)get_sub(); }
 
+  /// Add the source location from \p other, if it has any.
+  template <typename T>
+  T &with_source_location(const exprt &other) &
+  {
+    static_assert(
+      std::is_base_of<exprt, T>::value,
+      "The template argument T must be derived from exprt.");
+    if(other.source_location().is_not_nil())
+      add_source_location() = other.source_location();
+    return *static_cast<T *>(this);
+  }
+
+  /// Add the source location from \p other, if it has any.
+  template <typename T>
+  T &&with_source_location(const exprt &other) &&
+  {
+    static_assert(
+      std::is_base_of<exprt, T>::value,
+      "The template argument T must be derived from exprt.");
+    if(other.source_location().is_not_nil())
+      add_source_location() = other.source_location();
+    return std::move(*static_cast<T *>(this));
+  }
+
 protected:
   exprt &op0()
   { return operands().front(); }

src/util/std_expr.h

@@ -1571,6 +1571,16 @@ class array_exprt : public multi_ary_exprt
   {
     return static_cast<array_typet &>(multi_ary_exprt::type());
   }
+
+  array_exprt &with_source_location(const exprt &other) &
+  {
+    return exprt::with_source_location<array_exprt>(other);
+  }
+
+  array_exprt &&with_source_location(const exprt &other) &&
+  {
+    return std::move(*this).exprt::with_source_location<array_exprt>(other);
+  }
 };
 
 template <>

src/util/string_constant.cpp

@@ -53,8 +53,5 @@ array_exprt string_constantt::to_array_expr() const
     *it = from_integer(ch, char_type);
   }
 
-  if(source_location().is_not_nil())
-    dest.add_source_location() = source_location();
-
-  return dest;
+  return std::move(dest).with_source_location(*this);
 }